1. Field of the Invention
The present invention relates to a system for truncated decay or monophonic pedal in an electronic musical instrument.
2. Description of the Prior Art
Although it is generally desirable to allow two or more notes to be played simultaneously on one keyboard of an electronic musical instrument, there are situations when more than one note at a time is unwanted. An example of such a situation is in the imitation of a wind instrument which is capable of sounding only one note at a time. Another example arises when playing the pedal notes of an electric organ. There, the simultaneous generation of two or more low notes might produce an unmusical sound.
In the past, various approaches have been used to limit the number of tones that can be produced simultaneously. Typically these systems were associated with the pedal keys of an electronic organ or with a pedal clavier. Often they involve the immediate truncation of a sustained or decaying tone as soon as the next pedal key is depressed. For example, in the U.S. Pat. No. 2,480,132 to Hammond, there is disclosed a pedal clavier in which each pedal-operated switch is maintained in operated condition and released only upon the depression of another pedal. In this type of instrument, the tone of the last depressed pedal persists with gradual decay until a second pedal is depressed.
In the U.S. Pat. No. 3,227,799 to Holman, the playing of one note on the pedal board cuts off sustained playing of any other note. To accomplish this, Holman uses a tone gating system in which the tone generator for each note is connected to a common output via a respective diode. When a particular note is selected, the corresponding diode is forward biased by a negative voltage from an associated capacitor that is rapidly charged via a neon bulb associated with the selected note. Cancellation of all other notes is accomplished by simultaneously applying a high positive voltage to all of the remaining neon bulbs. This causes these neons to fire and to apply a positive potential to the corresponding capacitors, thereby biasing the corresponding diodes off. No other tone then is gated to the common output.
In the electronic musical instrument disclosed in U.S. Pat. No. 3,446,904 to Brand, a selected tone gate is maintained open after key release by the charge on an associated capacitor. The decay time is determined by the value of this capacitor and a resistor that is common to all of the gate decay circuits. Truncation of a decaying note is accomplished by a killer circuit that momentarily short circuits all of the capacitors, thereby discharging them and terminating their maintaining action on the corresponding tone gates.
A similar technique for accomplishing sustain and cancellation of sustain upon playing of a subsequent pedal is disclosed in the U.S. Pat. No. 3,480,719 to Schwartz. There, too, a slowly discharged capacitor is used to control the sustain. If the capacitor is still charged, so that the previous note is still decaying when a subsequent note is played, a transistor switch circuit is turned on to discharge the capacitor in very short order, thereby cancelling the note that was decaying. A similar technique is employed in the sustain tone device disclosed in U.S. Pat. No. 3,519,723 to Wiest. There, a knock-off circuit is provided for discharging the capacitors associated with the time-delay tone sustain circuit, so that a note can be abruptly terminated when a subsequent key is depressed.
Another type of monophonic pedal system is disclosed in the U.S. Pat. No. 3,585,892 to Nakajima et al. In this type of system, if two or more keys are simultaneously depressed, only the selected tone having the lowest or highest frequency is generated. This is accomplished by using a set of tone gates connected across a power supply in ascending order according to the note frequencies. If two or more keys are depressed, only the normally non-conducting switching device closest to the power supply becomes conductive so as to open the corresponding highest or lowest frequency key gate.
In the U.S. Pat. No. 3,882,751 to Tomisawa et al, a time-shared system is shown in which a monophonic pedal effect is achieved by restricting the assignment of pedal keys to only one channel. Thus if a second pedal key is depressed, there is no channel available, and it will not be sounded. A decay truncation circuit permits the subsequent pedal note to be assigned to the one channel if the prior key has been released and is in the process of decay.
It is an object of the present invention to provide a monophonic pedal or truncated decay system for an electronic musical instrument. Another object is to provide such a system for a time-shared musical instrument, advantageously but not necessarily of the digital tone generation type.
A further object of the present invention is to provide a decay truncation system that is effective only after one of the notes has been released. That is, if two or more keys are depressed simultaneously, both will sound. However, as soon as one is released, its tone will not decay, but will be truncated immediately. Similarly, if only a single decaying tone is being generated, this tone will be truncated immediately upon depression of the next key.